1. Field of the Invention
The present invention generally relates to a reefing system for parachutes.
2. Description of the Related Art
Parachutes are typically used in emergency life support situations. Parachutes also provide a means to deliver cargo and supplies to inaccessible regions and to quickly supply military troops. Materials with high strength-to weight-ratios are the standard for parachute design and construction. The performance of most parachutes with respect to deployment altitudes and velocities is limited due to the relatively small variety of materials that have the required high strength-to weight-ratios. Increasing deployment altitudes requires increases in aircraft true airspeed due to reduction in atmospheric density. This translates to faster opening of the parachute canopy and relatively higher forces placed on the entire parachute system. In order to ensure parachute system survival under these conditions, reefing techniques were developed to slow the opening of the parachute canopy to allow the parachute system to remain within its narrow performance envelope. Two commonly used reefing techniques are parachute canopy skirt reefing and parachute suspension line reefing. Canopy skirt reefing is illustrated in FIG. 1. Parachute system 10 comprises canopy 12 which has canopy skirt 14. Parachute system 10 also includes suspension lines 16 that are attached to canopy 12 and payload 18. Parachute system 10 employs a reefing cord 20 that has a predetermined circumference that translates to a diameter that is less than the full, inflated diameter of canopy skirt 14. Cord 20 is attached to canopy skirt 14 by sliding it through reefing rings permanently attached to canopy skirt 14 at each suspension line junction. Reefing cord 20 forces the parachute to inflate to a relatively small diameter so as to decelerate parachute system 10 to a lower velocity. Reefing cord 20 maintains parachute system 10 within its designed performance parameters prior to the occurrence of either the next reefing stage or total disreef. Disreefing is typically initiated by the use of expensive time-delay pyrotechnics. In the case of multi-stage reefing, multiple pyrotechnic devices are used.
Referring to FIGS. 2A and 2B, there is illustrated two suspension-line reefing techniques. Suspension line reefing techniques prevent full inflation of the parachute canopy by grouping the suspension lines together at some calculated distance below the parachute canopy skirt to first allow inflation to a particular diameter and drag area, and then allow disreefing to a larger diameter or full opening of the canopy. Line reefing can be initiated through the use of either expensive time-delay pyrotechnics or a sail slider. FIG. 2A shows parachute system 30 which employs a pyrotechnic-type line reefing technique. Parachute system 30 comprises canopy 32, suspension lines 36, and line-reefing device 38. Canopy 32 includes canopy skirt 40. Suspension lines 36 are attached to payload 42. Line-reefing device 38 is a pyrotechnic-type device that operates on a time delay. FIG. 2B shows parachute system 50 which employs a sail slider. Parachute system 50 comprises canopy 52, suspension lines 56, and sail slider 58. Sail slider 58 includes a sail portion (not shown) which is well known in the art. Canopy 52 has canopy skirt 60. Suspension lines 56 are attached to payload 62. Sail slider 58 comprises a piece of material that has an opening on its perimeter through which suspension lines 56 pass so as to allow sail slider 58 to slide up and down suspension lines 56. As the parachute is opening, the sail portion (not shown) of sail slider 58 inflates while parachute canopy 52 is inflating. The inflation of parachute canopy 52 causes parachute skirt 60 and suspension lines 56 to spread open thereby forcing sail slider 58 down suspension lines 56 toward payload 62. The inflated sail portion (not shown) of sail slider 58 creates resistance to the downward, sliding movement of sail slider 58 thereby resisting the opening of parachute canopy 52 and slowing down the parachute opening. Sail slider 58 also provides a drag surface that acts as a drogue chute to initially reduce the deployment velocity of parachute system 50. Sail slider 58 also deflects the air stream outward so as to facilitate inflation of skirt 60 of parachute canopy 52.
The prior art reveals several different parachute reefing systems. U.S. Pat. No. 2,995,323 discloses a mechanical device for controlling the reefing and dereefing of a parachute canopy. U.S. Pat. No. 3,642,237 discloses a spiral, reefed, variable drag parachute. Reefing lines are formed about the body or canopy of the parachute in a spiral configuration to control the opening shock and rate of descent of the parachute. U.S. Pat. No. 3,278,143 discloses a parachute canopy that comprises reefing located at the panel centerline of the parachute. Reefing rings are secured to a reinforcing band and the lower inside edge of the canopy at the mid-points between the adjacent connected seams of the panels. U.S. Pat. No. 4,065,079 discloses a parachute having a reefing device that secures together spaced parts of the parachute canopy in order to provide a parachute canopy that is reduced in size. The parachute includes a release device for releasing the reefed section of the canopy after initial parachute development to allow the reefed section to inflate in full deployment of the canopy. U.S. Pat. No. 4,623,109 discloses a low altitude parachute system. The parachute comprises an annular ring parachute canopy that has a control vent. A restraining device is connected to the canopy which slows the opening of the central vent while the canopy inflates during deployment of the parachute. A pilot chute is connected to the restraining device. When the pilot chute is inflated, it applies a force to the restraining device to slow the opening of the control vent. U.S. Pat. No. 4,624,427 discloses a parachute canopy reefing technique that utilizes a reefing buffer. The reefing buffer is attached to one of the parachute's suspension lines and encircles all of the suspension lines. The reefing buffer includes a pocket sewn into the buffer which holds a cutter in place. U.S. Pat. No. 4,697,765 discloses a parachute reefing/release device that uses an electro-explosive activator. U.S. Pat. No. 4,863,119 discloses a parachute reefing system that comprises an annular flexible membrane that has a centrally located vent opening and a plurality of guides spaced around the membrane. U.S. Pat. No. 4,955,563 discloses an apparatus for controlled, simultaneous opening of clustered parachutes. Each parachute in the cluster includes a canopy, a plurality of reefing rings attached to the skirt portion of the canopy and a plurality of suspension lines. U.S. Pat. No. 5,205,517 discloses a parachute system that comprises a large parachute that has an inlet control parachute. The large parachute has a main canopy which is reefed to the outer portion of the inlet control parachute. The inlet control parachute is operable to expand the inlet area of a large parachute. U.S. Pat. No. 5,209,436 discloses a parachute that has radial reefing means for use in packing and opening the parachute canopy in a controlled manner. The parachute has a circular canopy that has a peripheral skirt and a plurality of spaced radials. Reefing rings are attached to each of selected, non-adjacent radials. Published Application No. US2003038215 discloses a cruciform parachute assembly. The parachute comprises a slider and a series of reefing rings that are fixed to the canopy crown portion. U.S. Pat. No. 6,669,146 discloses a parachute cluster assembly and a method for providing gliding and trajectory control of the parachute assembly. British Patent No. GB 776296 discloses a parachute releasing or disreefing device that comprises a member that restrains the parachute from fully opening. This member is adapted to be broken by a chemical explosive means. U.S. Pat. Nos. 6,328,262 and 6,520,453 disclose various methods for forming a parachute.
What is needed is a new and improved reefing technique that safely and effectively controls the inflation of a parachute.